Potentially it is a great card bath practicably it is rarely useful.
Like DPsycho said there are lots of times when it would be useful but little times when you actually have it in your hands because of its rarity.
And on top of that it has a high cost of 23 gems and cant help you wherry much if you are in a fix with little resources or if your opponent has low wall as well.
All this makes Wall shift less practical and less desirable then any other last minute rescue cards like Order of the White Lotus, Overlord, Return to the beginning, Two towers ...
In my opinion this card should be changed from a rare card to an uncommon.